DE filters are the most effective form of domestic pool filtration available, guaranteeing the ultimate in pool water clarity. The secret behind the effectiveness of DE filters is the filter media itself. Water passes through extremely fine, highly porous Diatomaceous Earth (DE) which filters out the finest particles. Diatomaceous earth is a porous powder with microscopic openings, that, when magnified, look like tiny sponges. Clear water can pass through these openings, but particles, as small as one to three microns, are trapped during the first pass through the media. D.E. filters have internal elements that become coated with D.E. It is this ‘filter cake’ that strains dirt, dust, algae, and some forms of bacteria from the water.